Simple RIP Question

mzinz

Suppose we have the following topology:

R1

---

R2

---

R3

All routers are configured to run RIPv1.

Would it be more ideal/optimal for:
R1 sends advertisements only to R2,
R2 sends advertisements to R1 & R2,
R3 sends advertisements only to R2.

Or would it be more ideal to have all three routers send advertisements to all others?

rossonieri#1

hello mzinz,

from the picture - well it is how it goes right?
unless you have more interfaces connected to each router and specify which inactive (passive) routing interface..

if you have tried using dynamips probably you will encounter a massive routing updates broadcast - especially if create 2 or more ethernet interfaces plugged into 1 swiitch. i mean that you have created a dozen of routers with ethernet interfaces - split them into 3 or more computers..


cheers.

Spur

Your setup is a very "fixed" setup, but generally if you consider R2 as a hub router you would want to use default routes on R1 and R3. That would be the most optimal.

Webmaster

Implementing RIP is not on the BSCI exam so I moved this topic to the CCNA forums because it'll be more useful there.

mzinz

Let me rephrase what I was asking, specifically:

When using RIP, should routers only advertise to *directly connected networks*, or to all networks in an AS which are running the RIP protocol?

I included the example above because I was wondering: If R1 only sends updates to R2, then will R2 automatically forward the updates it received from R1 to all networks it is advertising on?

Spur

mzinz wrote:

I included the example above because I was wondering: If R1 only sends updates to R2, then will R2 automatically forward the updates it received from R1 to all networks it is advertising on?

Yes, R2 will send updates recieved from R1 on other active interfaces unless some of them are defined as passive. There is no way R1 will communicate directly with R3 via RIP.

mzinz

Thank you.

Webmaster

It won't actually forward updates as in relaying them. RIP routers broadcast their entire routing table to all neighbors, so that includes routes they received from 'other' neighbors. Before it sends updates however, it will increase the hopcount metric with 1.

Check the links I posted here for more info:
www.techexams.net/forums/viewtopic.php?t=21686

NightShade1

Look rip works by filling their routing tables....

ill give you a fast example

R1

---

R2

---

R3

---

R4

R1-R2 link has the network 10.1.1.0 network
R2-R3 link has the network 10.1.2.0 network
R3-R4 link has the network 10.1.3.0 network

In the beggining before sending the broadcast of their full routing table they will be like this
Router 1 table
10.1.1.0 directly connected

Router 2
10.1.1.0 directly connectd
10.1.2.0 directly connected

Router 3

10.1.2.0 directly connected
10.1.3.0 directly connected

Router 4
10.1.3.0 directly connected

They start exchanging routing updates so they will start filling up their routing tables

Router 1
10.1.1.0 directly connected
10.1.2.0 via 10.1.1.1 hop 1

Router 2

10.1.1.0 directly connectd
10.1.2.0 directly connected
10.1.3.0 via 10.1.2.1 hop 1

Router 3

10.1.2.0 directly connected
10.1.3.0 directly connected
10.1.1.0 via 10.1.2.2 hop 1

Router 4

10.1.3.0 directly connected
10.1.2.0 via 10.1.3.2 hop 1

they will keep filling up
Remenber they keep sending updates every 30 secs so in the next 30 secs he will see the router 2 has new updates in his routing table and will sent it to router 1(note that it will keep sending updates even if it has NOTHING new on it every 30 secs)
This is why this protocol blows it uses lot of CPU so a cpu overloading might occur


Router 1
10.1.1.0 directly connected
10.1.2.0 via 10.1.1.1 hop 1
10.1.3.0 via 10.1.1.1 hop 2

Router 2

10.1.1.0 directly connected
10.1.2.0 directly connected
10.1.3.0 via 10.1.2.1 hop 1


Router 3

10.1.2.0 directly connected
10.1.3.0 directly connected
10.1.1.0 via 10.1.2.2 hop 1

Router 4
10.1.3.0 directly connected
10.1.2.0 via 10.1.3.2 hop 1
10.1.1.0 via 10.1.3.2 hop 2


I bolded the ones that in the next 10 seconds had a new update.... the others receive the update but since they got nothing new to add they stay with what they got...

Hope this mini tutorial i did helps [/b]

Spur

Just to fill in.. Cisco uses triggered updates with RIP allthough this is not a RIP standard. Normal update cycle is every 30 seconds..

NightShade1

yep my mistake... guess my memory is blowing hehe yeah its 30 secs for rip, and is 10 secs for appletalk RTMP i have been reading too much and i got too much info in my head

ill edith my meesage thanks for correcting that part Spur

Spur

Don't worry.. My mind is messed up all the time

Right now I'm preparing for BCRAN and going over VPN stuff.. My head hurts of all the cramming..